The venoms of the red diamond rattlesnake (Crotalus ruber ruber), the sidewinders (Crotalus cerastes ssp.) and the three "mitchs" (Crotalus mitchelli mitchelli, C. m. stephensi and C. m. pyrrhus) will be studied for their chemical and certain of their physiopharmacologic properties. Fractions of the venome will be isolated, purified and characterized by gel filtration, ion exchange chromatography, qualitative and quantitative gell electrophoresis, ultrafiltration, ultracentrifugation, amino acid analysis and, in the case of peptides, amino acid sequencing. The LD50 of each fraction will be determined and those fractions which prove more lethal than the crude venom, or have relatively similar LD50 values, will be studied for their effects on nerve-muscle preparations, the central nervous system, and the cardiovascular system. Studies will also be made on certain coagulant-anticoagulant properties of the venom fractions, as well as on immunological phenomena. Consideration will be given to the chemical and pharmacological evolution of those venom fractions that appear to have a specific affinity for the nervous system, while attempting to correlate this evolution with the anatomical changes that occurred in the venome apparatus. Finally, as in the past, attention will be given to the reole of these venom fractions as possible tools in biology, particularly in membrane transport, and as durgs in clinical therapeutics.